Silver cyanide plating baths have long been employed and afford significant advantages from the standpoint of commercial plating processes. However, over the years, there have been substantial efforts to develop noncyanide or low cyanide silver plating baths; generally such baths have often been uneconomical to operate or have resulted in dull deposits or have been slow in rate of electrodeposition.
Exemplary of efforts to produce a cyanide-free bath is Culjkovic U.S. Pat. No. 3,984,292 granted Oct. 5, 1976, which utilizes a thiosulfate bath and which uses sulfur or selenium as a brightener. Generally, such baths which are cyanide-free do not function as effectively as baths which complex the silver with cyanide.
In our copending Application Ser. No. 874,893 filed Feb. 3, 1978, now U.S. Pat. No. 4,121,982, we have disclosed a gold/silver alloy plating bath which has little or no free cyanide but which uses alkali metal silver cyanide as the principal source of the silver ion. In our work, we have found certain electrolytes can be combined with the alkali metal silver cyanide to enable us to limit to a very small amount the amount of free cyanide in the bath, thus minimizing some of the problems of toxicity due to fume evolution while at the same time obtaining the commercial advantages of a silver cyanide bath. In our copending application, we disclose the advantages of a selenium brightener in such a low cyanide bath.
It is an object of the present invention to provide a novel, simple bath for electroplating pure silver at varying rates of speed.
It is also an object to provide such a bath which is facile to produce and which may be readily maintained.
Another object is to provide a method for electrodepositing substantially pure silver upon conductive workpieces using such a novel bath and which method is simple, relatively easy to control, and substantially free from cyanide fume evolution.